The centre is set to stay with Connacht until the summer of 2025.
Aki first joined the westerners in 2014 and helped the province win the PRO12 title in 2016.
He made his Irish debut in 2017, and was a central player to Ireland's Grand Slam win back in March.
He has been nominated for this year's World Player of the Year award, alongside Irish coach Andy Farrell up for Coach of the Year gong.

Monday Morning Sports Update
Sunday Evening Sports Update
Mourinho's Benefica Go Unbeaten but Miss Title
Brave Kildare Fall Short in Leinster Ladies Final
Chelsea Appoint Xabi Alonso as New Manager
Conor McGregor Set for UFC Return in July
Manchester City Complete Double with FA Cup Win
Moylan Hat-Trick as Ireland Hit Five Past Grenada